The present invention relates to composite components comprising an unfoamed polymer phase and a foamed phase, and to a process for producing the same.
Composite components composed of at least two different components are known in the prior art. For the purposes of the present disclosure, the expression “composite component” relates to a component made of two or more connected materials. Examples of conventional composite materials are carbon-fiber-reinforced plastic and glassfiber-reinforced plastic.
For the purposes of the present invention, foam is composed of small gas bubbles separated by solid walls or by flexible walls.
Examples of foams are inter alia:                pumice, a porous glassy volcanic rock with density lower than that of water        foams, foam rubber, and polystyrene as material for insulation and for packing        foamed glass        aerogels        metal foams, e.g. aluminum foam for metal structures which have high strength but low weight        foamed concrete.        
When a polyamide is combined with a foam the result is a sandwich foam in the context of fiber-composite materials.
JP 59169833 A describes a process for producing a composite product where a high-viscosity plastics composition is cast into a mold.
M. T. Penny, Cellular Polymers (1988), 7 (2), pp. 119-133 describes the production of nylon foams via “reactive injection molding” (RIM).
JP 63069614 A describes the production of synthetic resin from a plurality of layers, where the inner layer is composed of polyurethane (PU) and the outer layer is based on caprolactam.
JP 7195602 A and JP 2826059 B2 describe moldings composed of a foamed core based on PU and an external layer comprising nylon and carbon fibers, where the core and the external layer are connected to one another by heating.
However, the composite materials of the prior art, and the processes for producing the same, have certain disadvantages. By way of example, the materials known hitherto mostly have relatively high weight. Furthermore, the materials of the prior art are mostly adhesive-bonded; the result is often inadequate adhesion between various components. In many instances moreover there is a risk with the processes previously described that the foam component will be damaged or destroyed during the course of processing, because high pressure is needed.
It was therefore an object to achieve a further reduction in the weight of a composite component in order to provide genuinely lightweight materials, while nevertheless ensuring good adhesion between various components and moreover maintaining as far as possible the stiffness of the product. The foam which is a constituent of a composite component here should not be damaged during production of the composite component.
Surprisingly, said object has now been achieved by production of an unfoamed polymer phase via anionic polymerization in the presence of a foamed phase.
The present invention therefore provides a process for producing a composite component, comprising at least one unfoamed polymer phase (P) comprising polyamide, and at least one foamed phase (G), where the unfoamed phase is produced via anionic polymerization of at least one monomer (M) selected from the group of the lactams in situ in the presence of the foamed phase (G).
The present invention further provides a composite component that can be produced by the process of the invention, and also provides the use of a composite component that can be produced by the process of the invention, as structural element in automobile construction.
In one preferred embodiment of the process of the invention, the foamed phase (G) is a closed-cell phase.
For the purposes of the present disclosure, the expression “closed-cell foam” relates to foams in which the cells do not have pores or disrupted areas. In contrast to this, the expression “open-cell” designates a foam structure defined by the presence of at least two pores or disrupted areas associated with each cell. Furthermore, the majority of the cell lamellae must belong to at least three cells. Production of closed-cell foams is generally based on polyurethane (PU), polyvinyl chloride (PVC), polymethacrylimide (PMI), and polystyrene (PS) (see Arnim Kraatz, Dissertation 2007, University of Halle).
In the invention, the unfoamed polymer phase (P) is preferably produced via anionic polymerization of at least one lactam monomer by way of reactive injection molding (RIM).
A description of the RIM process for producing polyamide moldings, and of the necessary apparatuses, is found by way of example in P. Wagner, Kunststoffe 73 (1983), 10, 588-590, and also in P. Schneider et al., Plastics Engineering, 1984, pp. 39-41.
The at least one monomer (M) in the process of the invention is one selected from the group of lactams. By way of example, it is possible to use monomers from the group consisting of caprolactam, piperidone, pyrrolidone, laurolactam, and mixtures of these. Preference is given to use of a monomer (M) selected from the group comprising caprolactam, laurolactam, and mixtures of these.
It is also possible to copolymerize up to 50% of lactones, preferably caprolactone, with the monomer (M) from the group of the lactams.
In one embodiment of the process of the invention, the anionic polymerization of the at least one monomer (M) is carried out in the presence of a catalyst (K) and/or of an activator (A).
An example of a suitable optional catalyst (K) is sodium caprolactamate, potassium caprolactamate, magnesium bromide caprolactamate, magnesium chloride caprolactamate, magnesium biscaprolactamate, sodium hydrides, sodium metal, sodium hydroxide, sodium methoxide, sodium ethoxide, sodium propoxide, sodium butoxide, sodium hydride, potassium metal, potassium hydroxide, potassium methoxide, potassium ethoxide, potassium propoxide, potassium butoxide, preferably sodium hydrides, sodium metal, sodium caprolactamate, and particularly preferably sodium caprolactamate (e.g. Bruggolen® C 10, a solution made of 18% by weight sodium caprolactamate in caprolactam).
Compounds suitable as optional activator (A) are inter alia aliphatic diisocyanates, such as butylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, decamethylene diisocyanate, undodecamethylene diisocyanate, dodecamethylene diisocyanate, and also aromatic diisocyanates, such as tolylene diisocyanate, isophorone diisocyanate, 4,4′-methylenebis(phenyl isocyanate), 4,4′-methylenebis(cyclohexyl isocyanate), or polyisocyanates, such as isocyanurates of hexamethylene diisocyanate, Basonat® HI 100 from BASF SE, allophanates, such as ethyl allophanate, and mixtures of these, preferably hexamethylene diisocyanate, isophorone diisocyanate, and particularly preferably hexamethylene diisocyanate. The diisocyanates can be replaced by monoisocyanates.
Compounds alternatively suitable as activators are aliphatic diacyl halides, such as butylenedioyl chloride, butylenedioyl bromide, hexamethylenedioyl chloride, hexamethylenedioyl bromide, octamethylenedioyl chloride, octamethylenedioyl bromide, decamethylenedioyl chloride, decamethylenedioyl bromide, dodecamethylenedioyl chloride, dodecamethylenedioyl bromide, and also aromatic diacyl halides such as tolylenedioyl chloride, tolylenemethylenedioyl bromide, isophoronedioyl chloride, isophoronedioyl bromide, 4,4′-methylenebis(phenyl)oyl chloride, 4,4′-methylenebis(phenyloyl bromide, 4,4′-methylenebis(cyclohexyloyl chloride, 4,4′-methylenebis(cyclohexyl)oyl bromide, or a mixture of these, preferably hexamethylenedioyl chloride, hexamethylenedioyl bromide, or a mixture of these, particularly preferably hexamethylenedioyl chloride. The diacyl halides can be replaced by monoacyl halides.
The molar ratio of lactam to the catalyst can vary widely, but is generally from 1:1 to 10 000:1, preferably from 10:1 to 1 000:1, particularly preferably from 50:1 to 300:1.
The molar ratio of activator to the catalyst can vary widely, but is generally from 100:1 to 1:10 000, preferably from 10:1 to 1:100, particularly preferably from 1:1 to 1:10.
The foamed phase (G) in the invention can by way of example take the form of a block, of a sphere, of a cylinder, or of a pyramid.
The foamed phase (G) is preferably composed of polyamide (PA). However, the foamed phase can also be composed of another material, for example of another plastic, or of metal or wood.
In one embodiment of the process of the invention, the foamed phase (G) forms a block, where at least 90%, preferably at least 95%, of the surface of a lateral area of the foamed phase (G) has been covered with the unfoamed phase (P).
In another embodiment of the process of the invention, at least 90%, preferably at least 95%, of the entire surface of the foamed phase (G) have been covered with the unfoamed phase (P).
In one embodiment of the process of the invention, the foamed phase (G) is introduced first into a mold, and then the unfoamed polymer phase (P) is cast into said mold.
The polymerization can also be carried out in the presence of crosslinking agents.
It is possible here to react a diisocyanate or a diacyl halide with a lactam A at a temperature of from (−30) to 150° C. and then to carry out reaction with a lactam B, with a catalyst, and with an activator, at a temperature of from 40 to 240° C. Diisocyanate here can be replaced by polyisocyanate, and diacyl halide here can be replaced by polyacyl halide.
The polymerization can take place in the presence of additives, such as fibers or fillers; the fibers here are preferably those selected from the group comprising glass fibers and carbon fibers. Said fibers can serve as fillers and/or reinforcing materials.
Examples of other fillers or reinforcing materials that can be used are minerals of grain size conventional for thermoplastics applications, examples being kaolin, calk, wollastonite, or talc, or glass fibers, e.g. ground glass fibers, and also textile structures (wovens and laid scrims) made of unidirectional fibers, preferably glass fibers and carbon fibers.
The foamed phase (G) can also have a structure, e.g. holes, grooves, or notches.
The composite component that can be produced in the invention can also comprise more than one foamed phase (G) and more than one unfoamed polymer phase (P). By way of example, the composite component that can be produced in the invention can comprise two layers of a foamed phase (G) and three layers of an unfoamed phase (P).
The final product of the process of the invention, i.e. the composite component that can be produced in the invention, preferably has, based on the entire final product, at least 20% by volume of the foamed phase (G), particularly preferably at least 50% by volume.
The composite component that can be produced by the process of the invention can inter alia be used advantageously as structural element in automobile construction.